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Unlock Faster, Smarter Power Quality Analysis
Interharmonics—signals that land between the 60 Hz fundamental and its integer harmonics—behave very differently from ordinary distortion. Because their frequencies do not “fit” neatly into one cycle, they create low-frequency envelopes that make root-mean-square (RMS) voltage swing within a single cycle and from cycle to cycle. The paper walks through a concise mathematical derivation showing how any pair of sine components produces new sum- and difference-frequency terms in the RMS calculation, then demonstrates the practical impact with a 175 Hz component riding on the line. In the worked example, that one off-frequency tone magnifies into a 5 Hz amplitude modulation large enough to push lighting past the irritability threshold of IEEE Std 141—a recipe for customer complaints and equipment
Key topics include:
- HRMS Effects
- Deriving the RMS-Variation Formula
Worked Example: 175 Hz Injection and Flicker Risk
Why utilities should care:
Light flicker is one of the most visible—and most reported—power-quality issues. The analysis in this white paper equips engineers with a clear, physics-based explanation of how seemingly small interharmonic sources such as drives, arc furnaces, or inverter-based resources can destabilize RMS readings, trip sensitive loads, and trigger costly customer claims. By understanding the math, utilities can set monitoring filters correctly, pinpoint culpable equipment faster, and justify mitigation investments with hard numbers instead of guesswork. In short, mastering interharmonics helps protect grid reliability, safeguard revenue, and strengthen customer trust.
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